Japanese Patent Application Publication No. 2001-350353 discloses a transfer current controlling during image formation. This publication discloses a technique for controlling a tandem-type configuration in which a black process unit is disposed at the most downstream position among a plurality of process units. When image formation is executed in the black-white mode, transfer currents are controlled such that the transfer current for black (K) is set to 12 microamperes (μA), and the transfer currents for yellow, magenta, and cyan are set to substantially 0 (zero) microampere (μA).